Digitally controlled analog devices include devices such as amplifiers. When used for audio, such devices often include multiple channels. An example of an audio power amplifier is a digital pulse-code modulation (PCM) input Class D power amplifier. Such amplifiers may support time division multiplexed (TDM) data and may also support I2S data. TDM is a type of multiplexing in which two or more bit streams or signals are transferred appearing simultaneously as sub-channels in one communication channel, but physically taking turns on the channel.
I2S (also known as Inter-IC Sound, Integrated Interchip Sound, and IIS) is an electrical serial bus interface standard used for connecting digital audio devices together, e.g. to communicate PCM audio data between integrated circuits. The I2S requires at least three lines: a bit clock line, a word clock line, also known as a word select (WS), channel sync or left-right clock or (LRCLK) line, and at least one multiplexed data line.
The I2S digital interface with BCLK, LRCLK, and DIN are commonly used in most digital audio systems. The interface allows for a multiple channels of data to be sent over the shared DIN line. Each frame of data is aligned with the LRCLK signal. The DIN data within that frame can be any number of TDM channels with any number of bit depths.
Devices (a/k/a “parts”, “output channels”, and the like) typically need to be programmed for the type of digital interface. Typically, a device will be programmed for the format of the TDM data using Inter-Integrated Circuit or “I2C” protocol. The I2C protocol uses two bidirectional, open-drain lines, known as the Serial Data Line (SDA) and the Serial Clock Line (SCL) that are pulled up with resistors to Vcc, e.g. 3.3 or 5 volts d.c. However, such programming of the data formatting can make the system more complex and, in some cases as described below, there may not be enough pins (a/k/a “leads”, “contacts”, “balls”, “pads”, etc.) to support an I2C interface for such programming.
Some audio amplifier integrated circuits (ICs) are quite small and include only a few contacts on the IC package. These small ICs are useful in compact electronic devices such as cellular telephones, tablets and notebook computers. For example, a small wafer level package (WLP) may have only nine contacts (sometimes called “pads” or “balls”) for interconnection with a printed circuit board. Providing I2C capabilities to such small packages can be problematical do to the limited number of available pads and, in some cases, there aren't enough contacts to support an I2C interface for the purpose of programming, even though an I2C interface only requires a couple of dedicated pins.
The problem of providing multiple data lines, such as I2S lines, to analog/digital devices having few leads, contacts, pads or the like extends beyond audio power amplifier devices, which were set forth only by way of example. The usual solution is to put such analog/digital devices in larger packages with more pins, which increases the form factor of the IC.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.